Beurre

Avoir beurre sur la tête. To be covered with crimes. Taken from
a Jewish saying, “If you have butter on your head (i.e. have
stolen butter and put it in your cap), don't go into the sun.” (Vidocq: Voleurs, vol. i. p. 16.)

J'y suis pour mon beurre.

Here beurre means argent: I paid for it through the
nose. Beurre or butter has the same relation to food as wealth
has to civil life; it does not take the place of it, and does not make
it, but it makes it go down more pleasantly, and adds somewhat to its
wholesomeness. As Shakespeare says, “Where virtue is, it makes more
virtuous.”

Promettre plus de beurre que de pain.

To promise much, but perform little. To promise more than one, can,
or chooses to, perform. The butter of a promise is of no use without
substantial bread. “Be thou fed” will not fill an empty stomach. A
little help is worth a deal of pity.